AD737

The AD737 is a low power, precision, monolithic true rms-to-dc converter. It is laser trimmed to provide a maximum error of 0.2 mV 0.3% of reading with sine-wave inputs. Furthermore,it maintains high accuracy while measuring a wide range of input waveforms, including variable duty cycle pulses and triac (phase) controlled sine waves.

The low cost and small physical size of this converter make it suitable for upgrading the per-formance of non-rms "precision rectifiers" in many applications.Compared to these circuits, the AD737 offers higher accuracy at equal or lowercost.The AD737 can compute the rms value of both ac and dc input voltages. It can also be operated ac coupled by adding one ex-ternal capacitor. In this mode, the AD737 can resolve input sig-nal levels of 100 m V rms or less, despite variations in temperature or supply voltage. High accuracy is also maintained for input waveforms with crest factors of 1 to 3. In addition, crest factors as high as 5 can be measured (while introducing only 2.5% additional error) at the 200 mV full-scale input level.

The AD737 has no output buffer amplifier, thereby significantly reducing dc offset errors occuring at the output. This allows the device to be highly compatible with high input impedance A/Dconverters. Requiring only 160 m A of power supply current, the AD737 is optimized for use in portable multimeters and other battery powered applications. This converter also provides a "power down" feature which reduces the power supply standby current to less than 30 m A.The AD737 allows the choice of two signal input terminals: a
12 high impedance (10 W ) FET input which will directly interface with high Z input attenuators and a low impedance (8 kW ) input which allows the measurement of 300 mV input levels, while operating from the minimum power supply voltage of +2.8 V,3.2 V. The two inputs may be used either singly or differentially. The AD737 achieves a 1% of reading error bandwidth exceed- ing 10 kHz for input amplitudes from 20 mV rms to 200 mV rms while consuming only 0.72 mW. The AD737 is available in four performance grades.

The AD737J and AD737K grades are rated over the commercial temperature range of 0 C to +70 C. The AD737A and AD737B grades are rated over the industrial temperature range of 40 C to +85 C. The AD737 is available in three low-cost, 8-lead packages: plas- tic DIP, plastic SO and hermetic cerdip.